This invention relates to a method of fabricating a sintered body containing tin oxide.
A film of pure tin oxide is electrically conductive and transparent and therefore finds wide application where these properties are required, for example as electrodes in liquid crystal displays and as optical coatings.
A film of tin oxide is conventionally deposited by sputtering from a target that comprises a sintered body of tin oxide. In order to avoid large, sharp spatial variations in the thickness of the film it is necessary that the ceramic target be of uniform density. It is desirable that the sputtering target be of high density in order for it to be cohesive and have a reasonable operational life.
A ceramic body of tin oxide having a density up to about 90% theoretical density can be made by hot isostatic pressing. However, it has been found that hot isostatic pressing sometimes leads to a target of non-uniform composition even though the ingredients have been thoroughly mixed before the pressing takes place.
When granular material is sintered, material diffuses across the grain boundaries with the result that contacting grains are drawn together and merge. It is known to use a sintering agent to promote the sintering operation. A sintering agent is liquid at the sintering temperature. The liquid sintering agent enters the space between grains and promotes diffusion across the grain boundaries. When the grains merge and are bonded together, the sintering agent is displaced.
A difficulty associated with sputtering a tin oxide film from a target of sintered tin oxide is that the resulting film might be colored due to reduction of the tin oxide. This can occur because the tin oxide in the sintered body is reduced by impurities in the sintered body or because sputtering takes place in a non-oxidizing atmosphere.
It is desirable that a film of tin oxide be stable, both with respect to the chemical agents that it contacts in use and with respect to time. The qualities of a sputtered tin oxide film can be improved by including antimony in the tin oxide sputtering target. In particular, the conductivity and stability of the film are improved by the presence of antimony, and the transparency of the film remains acceptable.